This invention is generally directed to magnetic nanocomposite compositions and processes for the preparation thereof, and more specifically the present invention is directed to ferrofluids comprising aqueous suspensions of magnetic nanocomposite compositions, silanated magnetic nanocomposite compositions, and mixtures thereof, comprised of, for example, Fe.sub.2 O.sub.3 nanoparticles and an ionic exchange resin. In embodiments, the ferrofluids of the present invention possess a high magnetization moments, for example, from about 20 to about 40 emu/gram, and a high "spike" or spicule forming property which renders the compositions useful for improving a variety of conventional ferrofluid properties and enables new applications thereof such as a liquid ink droplet ejection composition and system as illustrated herein.
The colored, nearly optically transparent aqueous magnetic ferrofluid compositions of the present invention are useful in magnetic applications, for example, magnetic imaging and printing with dry and liquid developer compositions, and for electrophotography, especially xerographic imaging and printing. Other applications of the ferrofluids of the present invention include: those disclosed in the prior art, reference for example, Magnetic Fluids Guidebook: Properties and Applications, V. E. Fertmann, Hemisphere Publishing Corp., N.Y., 1990, and other novel uses, such as, in a magnetically controlled charge transfer media and charging apparatus for a photoreceptor as disclosed in, for example, commonly assigned U.S. Pat. No. 5,457,523; in reversibly magnetically controlling the extent of exposed or spiked ferrofluid surface area; and as magneto-mechanical seals in, for example, hi-fi speakers and liquid printing apparatus.
The ferrofluid compositions of the present invention possess unique electrical, optical, magnetic, and chemical properties due primarily to the extremely small dimensions, for example, about 10 nanometers and below, of the nanocrystalline particles in the nanocomposite.
An important limitation to the preparation and maintenance of nanoscale materials has been the tendency of the initially small atomically clustered particles to aggregate into larger masses to reduce the energy associated with the high surface area to volume ratio of the nanosized particles. In the aforementioned U.S. Pat. No. 4,474,866, a polymeric matrix, for example, a synthetic ion exchange resin is used to prepare, stabilize, isolate, and characterize related nanocrystalline Fe.sub.2 O.sub.3 particles as a magnetic polymer composite. In the present invention, there are formulated various magnetic nanocomposites and ferrofluids thereof comprised of, for example, nanocrystalline particles of Fe.sub.3 O.sub.4, Fe.sub.2 O.sub.3, and the like magnetic metal oxides, and ionically active resin matrices. The nanocomposites are subsequently processed in accordance with the present invention to form high magnetization aqueous ferrofluid formulations.
Prior art formation of submicron or nanometer structures have predominantly included the formation of large particles which are subsequently ground or milled until particles of the desired size are achieved. The grinding and milling times associated with the formation of such particles ranged from 120 to about 2,900 hours. A method of forming dry magnetic submicron particles by precipitation of a magnetic oxide in an ion exchange resin is exemplified by Ziolo in the aforementioned U.S. Pat. No. 4,474,866. According to the method employed therein, an ion exchange resin is loaded with a magnetic ion and chemically converted to a magnetic oxide Fe.sub.2 O.sub.3. The resulting magnetic iron oxide loaded ion exchange resin is then recovered and dried. The magnetic polymer resin is then optionally micronized to form a fine magnetic powder.
The following patents are of interest:
U.S. Pat. No. 5,013,471 to Ogawa, issued May 17, 1991, discloses a magnetic fluid, a method for the preparation thereof, and a magnetic seal apparatus using the same, characterized in that the surfaces of ferromagnetic particles are covered with a monomolecular adsorbed film composed of a chloro-silane type surfactant, and the coated particles are dispersed in an oil.
U.S. Pat. No. 5,354,488 to Shtarkman et al., issued Oct. 11, 1994, discloses a rheological fluid composition which is responsive to a magnetic field. The composition comprises a vehicle, magnetizable particles suspended in the vehicle, and a dispersant. The dispersant comprises particles having no dimension greater than 10 nanometers. The dispersant is preferably carbon.
U.S. Pat. No. 4,992,190 to Shtarkman et al., issued Feb. 12, 1991, discloses a rheological fluid composition which is responsive to a magnetic field. The composition comprises magnetizable particulate, silica gel as a dispersant and a vehicle. A preferred magnetizable particulate is insulated, reduced carbonyl iron. The silica gel has an average particle size, typically, of about 0.05 micrometers.
U.S. Pat. No. 5,219,554, to Gorman et al., issued Jun. 15, 1993, discloses hydrated biodegradable superparamagnetic metal oxides exhibiting certain magnetic and biological properties suitable for use as magnetic resonance imaging agents to enhance magnetic resonance images of animal organs and tissues. Certain metal oxides which can be superparamagnetic are in the form of dispersoids or fluids which employ carrier fluids which are physiologically acceptable and are uncoated or surrounded by a polymeric coating to which biological molecules can be attached. Superparamagnetic fluids containing silanized iron oxides can be prepared by first subjecting the iron oxides to sonication to form oxyhydroxides, followed by the addition of the organosilane compound and further sonicated to disperse the materials, and thereafter, the silane is attached or associated to the surface via a dehydration reaction. The polymerization of the silane may occur before or after the deposition on the surface of the oxyhydroxide, reference col. 16, lines 38 to 46. Measured magnetic properties of certain superparamagnetic fluids at high magnetic field were nearly as magnetic as ferromagnetic iron oxide and far more magnetic than the paramagnetic ferric oxyhydroxide, showing high magnetic saturation. The fluids are superparamagnetic and lose virtually all of their magnetic moment in the absence of an applied magnetic filed, reference col. 29, lines 13 to 20.
The disclosures of each the above mentioned patents are incorporated herein by reference in their entirety.
There remains a need for high magnetization ferrofluids with high spiking or spicule forming properties and economical and convenient processes of obtaining very small magnetic particles and magnetic polymeric materials, and more specifically micron and submicron magnetic polymeric particles, without the complications and disadvantages encountered in the prior art.
Still further, there is a need for processes for the preparation of aqueous ferrofluids of highly magnetic nanocomposite particles that permit low cost, clean, and highly magnetic, ferrofluid formulations that can be selected as a magnetic liquid, and utilized in applications such as a additive component in dry or liquid electrophotographic developer compositions, carrier powder coatings, photoconductor pigment or resin coating suspensions, and as toner additives for enhanced photoreceptor development and cleaning.